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{-# LANGUAGE OverloadedStrings, QuasiQuotes #-}
module Y2017.M11.D24.Exercise where
Let's say, oh, that you're in a start-up, and you would like to, oh, return
a list of articles associated with a source article as JSON from a PostgreSQL
For example.
import Database.PostgreSQL.Simple
import Database.PostgreSQL.Simple.SqlQQ
import Database.PostgreSQL.Simple.FromRow
-- below imports available via 1HaskellADay git repository.
import Control.Scan.Config
import Store.SQL.Connection
import Store.SQL.Util.Indexed
import Y2017.M11.D01.Exercise -- for SpecialCharTable
import Y2017.M11.D03.Exercise -- for Strength
import Y2017.M11.D21.Exercise -- for Brief
This is the Brief format, but instead of filtering down to a set of articles,
these articles, and their scores are already provided for you in the database.
So this exercise eta-reduces to writing a FromRow-ish instance on Brief,
extracting data from multiple tables then cleaning up special characters as
we go.
recs4Stmt :: Query
recs4Stmt = [sql|SELECT recommended_article_id,hindsight_score
FROM recommendation WHERE article_id=?|]
recs4 :: Connection -> Integer -> IO [IxValue (Maybe Strength)]
recs4 conn artId = undefined
-- now, we need to get the rest of the data, given the recommendation ids,
-- from the article table
articleDataStmt :: Query
articleDataStmt = [sql|SELECT id,publish_dt,title,full_txt FROM article
WHERE id IN ?|]
-- then we marry the IxValue with the data returned here to get a Brief
articleData :: SpecialCharTable -> Connection -> [IxValue (Maybe Strength)]
-> IO [Brief]
articleData conn artIds = undefined
-- now we have to return those as JSON ... but we already know how to do that.
{-- BONUS -----------------------------------------------------------------
So, create an app that from an article id returns the set of recommended
articles as JSON
main' :: [String] -> IO ()
main' args = undefined
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